The white dust/powder is the phosphor that fluoresces (hence the name "fluorescent light") when an electrical charge is passed over it. It contains phosphorous and some mercury, and in some older phosphor formulations, cadmium and antimony. Today's lamps use rare earth minerals with the mercury/phosphorous to produce a better light spectrum than those old bulbs we all hated in the early 70's.

In a 4' long light tube, you're probably talking about 20 to 40mg of mercury in the phosphor, depending on make, age, etc. In a 8' long tube, you might be looking at 50mg of mercury. The "bang" the bulbs make is because they're under several PSI pressure.

Long story short: don't go snorting the white dust. Mercury is something that accumulates in your body like other heavy metals and attacks your nervous system (among other things). The issue is the concentration in your body - so a guy the size of you Rich could put away quite a bit of Mercury, but if you suddenly lost a lot of body mass (whether fat or muscle loss), the mercury distributed throughout the tissues in your body would re-distribute in your remaining body mass and the concentration goes up. I've known miners in NV who accumulated a fair bit of mercury over their careers in cleaning up and re-processing old tailings piles from the days before cyanide heap leaching, and they had to undergo chelation to remove the mercury from their body when their doctor put them on a diet and they had to lose weight in later years. Chelation isn't fun, but it is possible to remove mercury from your body.

There isn't enough in one or two bulbs that is going to send you to the ER unless you're deliberately snorting up all the dust.